Retinoids are vitamin A derivatives that regulate gene expression through activation of the nuclear retinoid receptors (RARs and RXRs). Due to their antiproliferative and differentiation inducing activities, retinoids have shown promise for the chemoprevention and treatment of cancer. Unfortunately, most natural and non-selective retinoid analogs cause considerable toxicity due to the activation of their nuclear receptors, which has limited their clinical use. One class of synthetic retinoid-related molecules with selective RAR activity has been described that display strong apoptotic activity in cancer cells and represent promising leads for the development of novel retinoid-like anticancer agents. The RAR3/2-selective agonist MX3350-1 and the pan- RAR antagonist MX781 are representative of this novel family of retinoid analogs, which are characterized by the presence of an adamantyl group. The mechanism of apoptosis induction by these molecules is not fully understood but several lines of evidence support that it is independent of RARs. These analogs are therefore classified as atypical retinoids and in this proposal we will refer to them as adamantyl arotinoids (AdArs). Our mechanistic studies indicate that MX3350-1 and MX781 induce apoptosis via unique mechanisms of action. Activation of the ASK-1/JNK stress pathway and caspase 9 activity are required for the induction of apoptosis by MX3350-1, whereas MX781 induces apoptosis via oxidative stress and activation of caspase 2. Moreover, MX781 inhibits IKK2 in vitro and in cell-based assays. Preliminary evaluation of a novel series of MX781 analogs demonstrates that we can use molecular modeling strategies to separate IKK2 and RAR activities. Some of the novel AdArs are stronger inhibitors of IKK2 with no RAR activity, and have improved anticancer activity; these compounds are expected to be more effective and less toxic in vivo. The main goal of this project is two fold. First, we will characterize the anticancer activity in vitro and in vivo of novel AdAr analogs with no RAR transactivation activity in prostate cancer cells. Second, we propose experiments to decipher the mechanism of action of active AdArs with an emphasis on signaling transduction pathways. The antiproliferative activity of AdArs alone or in combination with other chemotherapeutic agents will be tested in vitro against a panel of prostate cancer cell lines and normal prostate epithelial cells (aim 1). Aim 1 will also investigate the mechanism of apoptosis induction by novel AdArs. We will evaluate the chemopreventive activity of AdArs in TRAMP mice (aim 2). Aim 3 will examine the mechanism of JNK activation via oxidative stress by MX781-like AdArs. Aim 4 will explore the effect of active AdArs on the prostate cancer kinome using kinase assays on peptide microarrays. The projected mechanistic studies will enhance our understanding of AdAr action in prostate cancer cells and potentially identify novel signaling molecules that are targeted by AdArs. The latter will be essential for the future structure-based optimization of AdArs as novel anticancer agents. Moreover, the proposed in vivo studies with the novel AdAr analogs might result in novel retinoid- based therapeutic strategies for the prevention and treatment of prostate cancer. PUBLIC HEALTH RELEVANCE: Project Narrative The proposed studies are relevant to the development of novel retinoid-based anticancer drugs for the chemoprevention and treatment of prostate cancer. Retinoids have long been of interest in cancer research but limited efficacy in vivo and elevated toxicity has hampered their clinical applicability for the prevention and/or treatment of solid tumors. Evaluating the anticancer activity of novel AdAr analogs lacking RAR-mediated transactivation activity may identify compounds with improved in vivo efficacy and reduced toxicity. Furthermore, we propose mechanistic studies focused on protein kinases and signaling pathways that will impact our understanding of AdAr action in prostate cancer. This will encourage rational structure-based optimization efforts in the future to quickly advance the use of retinoid-like molecules into the clinic.